Positive displacement pumps are known for pressurizing a fluid, effecting a fluid flow, or combinations thereof. Positive displacement pumps may trap a fixed mass of fluid in a pumping chamber and then perform work on the fixed mass of fluid by deforming or displacing a boundary of the pumping chamber. Reciprocating positive displacement pumps include plunger pumps, piston pumps, and diaphragm pumps, for example.
Check valves on an inlet to the pumping chamber, an exit from the pumping chamber, or both, may at least partially define the pumping chamber. An inlet check may allow flow only in a direction into the pumping chamber via the inlet check valve, and a discharge check valve may allow flow only in a direction out of the pumping chamber via the discharge check valve.
U.S. Pat. No. 4,990,058 (hereinafter “the '058 patent”), entitled “Pumping Apparatus and Pump Control Apparatus and Method,” purports to address the problem of accurately metering liquids over an extended flow range. The '058 patent describes velocity and position profile generator means to achieve constant average flow rate despite acceleration and deceleration which occur in each extend and retract phase of a reciprocating pump cycle. The '058 patent further describes a pump control method including designating a selected flow rate at which fluid is desired to be output by the pump; identifying the position of the movable member of the pump; and generating a velocity value and a position value in response to the designated flow rate.
However, the flowrate control described in the '058 patent may not be consistent with the needs of some pumping applications. For example, other applications may be tolerant to variations in the flow rate, and may benefit more from tailoring the pumping cycle to achieve other operability goals, such as maximum flow delivery or energy efficiency, for example.
Accordingly, there is a need for improved positive displacement pumps and improved methods for controlling positive displacement pumps to address the aforementioned problems or other problems in the art.